Plate heat exchangers usually consist of a stack of plates defining passages for fluids.
In order to improve the heat exchange between the fluids, corrugated sheets known as fins can be “sandwiched” between said plates forming the heat exchanger. The resulting passages are closed on either side by side bars. Once assembled, the heat exchanger is brazed to give the assembly mechanical strength and improved thermal contact.
Prior art heat exchangers are capable of exchanging heat between many fluids. It is common to find plate heat exchangers handling more than five fluids.
However, being highly compact, plate heat exchangers are also used in processes using only two fluids. Typically, this type of exchanger corresponds to an evaporator-condenser. In this configuration one fluid is evaporated by extracting heat from a second fluid which condenses.
If the brazing of the side bars of the evaporation passages is of poor quality, a leak can develop between a condensation passage and an evaporation passage. This reduces the purity of the fluid to be evaporated. In some processes this purity is critical, and such a leak can necessitate repairing or changing the plate heat exchanger.
One option would be to repair a heat exchanger by sealing off the leaky evaporation passage by closing it at the inlet and outlet and leaving this leaky passage in contact with the condensation passage, to which it is directly adjacent. The pressures between the two passages would thus equalize.
Traditionally, the condensation passages operate at pressures above those of the evaporation passages. Plate heat exchangers must therefore be designed so that the evaporation and condensation passages can withstand an identical pressure. Such a plate heat exchanger design increases the cost without any concomitant improvement in the thermal performance of said exchanger.
It is an object of the present invention to provide a method for repairing a plate heat exchanger that does not require a particular design of said exchanger.